Historically, transport networks for transporting large amounts of data have been based on Time Division Multiplexing (TDM). Increasingly, however, packet-switched networks are replacing TDM networks because of their ability to handle data traffic like ETHERNET or Internet Protocol (IP) data in a more optimised and flexible way.
In particular, connection-oriented packet-switched (CO-PS) networks have been proposed for the migration from legacy networks towards all-packet networks. CO-PS networks combine the flexible data routing and statistical behaviour of the packet switched network with guaranteed end-to end connection performance, monitoring manageability and end-to end resilience.
In order to provide end-to end connection performance between two nodes of a network, CO-PS networks establish a working path through the network between the two end nodes via a plurality of intermediate nodes, through which data traffic (generally packets) are routed. In addition, a standby path through the network between the two end nodes is also established. The status of the working path through the network is monitored using network Operation Administration and Maintenance (OAM) tools and protection mechanisms, and if a fault with a node of the network or a fault with a link between two nodes of the network is detected, the data traffic is switched from the working path to the standby path of the network in order to maintain the connection between the end nodes.
One common network protection mechanism that enables a fault within a link or a node of the network to be detected is the use of OAM Continuity check (CC) packets. These OAM CC packets are periodically sent along the working path, and typically also along the standby path, and their receipt is monitored to determine whether the working path and the standby path are operational. If OAM CC packets are not received through the working path, the data traffic packets are switched to the established standby path. Generally, it is required that switching to the standby path after detection of a fault is accomplished quickly, typically within a period of the order of 50 ms.
Commonly the working path established between two end nodes may traverse a number of different networks. In addition to protection mechanisms associated with a network layer established between the end nodes, each network may have its own protection mechanisms associated with a network layer established for that network. In a situation where a number of network types co-exist and inter-work to provide a data traffic service, the operation of the different network layers' protection mechanisms may result in instability of the network as a whole, or may result in a delay in providing protection against faults.